This PR moves `MergeConsecutiveExtractSlice` from `MergeConsecutiveInsertExtractSlicePatterns.cpp` to `FoldTensorSubsetOps.cpp`, and removes the duplicate `MergeConsecutiveInsertSlice` pattern in favor of `InsertSliceOfInsertSliceFolder`, which already exists in `FoldTensorSubsetOps.cpp` and provides equivalent functionality with greater stability. Since the merge-related patterns have been fully migrated out, `MergeConsecutiveInsertExtractSlicePatterns.cpp` is renamed to `DropRedundantRankExpansionPatterns.cpp` to better reflect its remaining responsibilities.
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